In my townhouse in Bangkok, the top of the stairwell that goes out to the roof gets very hot. I was thinking about installing one of those roof turbines that spin with the wind to pull some of the hot air out. I was wondering if anyone had any experience with these turbines. The roof above the stairwell is flat so I am a little worried about rain leaking in. Also, will it even help remove the hot air? At first, I was planning on putting in a power roof vent, but I keep reading those will pull too much air out along with the cooler air-conditioned air. The space at the top of the stairs is about 3.5 x 3.5 meters.

In my townhouse in Bangkok, the top of the stairwell that goes out to the roof gets very hot. I was thinking about installing one of those roof turbines that spin with the wind to pull some of the hot air out. I was wondering if anyone had any experience with these turbines. The roof above the stairwell is flat so I am a little worried about rain leaking in. Also, will it even help remove the hot air? At first, I was planning on putting in a power roof vent, but I keep reading those will pull too much air out along with the cooler air-conditioned air. The space at the top of the stairs is about 3.5 x 3.5 meters.

Not sure where you're from but these are used in California to vent attics. They move a lot of air if there is a nice breeze. I found the below estimates from a website:

"A small 12 inch diameter turbine vent with a constant wind speed of 5 miles per hour (mph) can remove 347 cubic feet of air per minute (cfm) from the attic space. A single 14 inch diameter turbine vent that is subjected to 15 mph winds can expel up to 1,342 cfm of air! If the winds are still, the vents still allow air to drift up and out of the attic space, although not nearly as much."

That would be way too much air if you're worried about pulling out the air conditioned air. You could probably get away with a simple vent without the turbine. They are basically a vertical pipe with a larger diameter cover raised over them so the air can flow by them, but rain can't fall in. Air blowing over the end of the pipe will pull the air out, but not nearly as much as a wind turbine.